This invention relates to glass-forming liquid crystals (GLC) and, more particularly, to liquid crystalline compositions comprising compounds having a molecular weight in the range of about 1000 to 5000 grams per mole, and to optical devices formed therefrom.
Liquid crystallinity is a consequence of spontaneous molecular self-assembly into a uniaxial, lamellar, helical, or columnar arrangement on a macroscopic scale. Because of their unique optical properties, liquid crystals are potentially useful as optical, photonic and optoelectronic devices (see for example Collings, P. J., and Patel, J. S., Handbook of Liquid Crystal Research, Oxford University Press, New York, 1997). In some of these applications, such as liquid crystal displays, the material functions in the fluid state where an applied field induces molecular reorientation with a response time on the order of milliseconds. With judiciously designed structural moieties, liquid crystals may also function in the solid state via a photonic or electronic stimulus with a much shorter response time. In addition, liquid crystals can be employed as passive devices in which no switching is involved. With the exception of applications in which molecular reorientation with an applied field is the basis, vitrified liquid crystals with an elevated glass transition temperature, Tg, offer long-term mesomorphic stability as well as environmental durability. Whereas glass formation appears to be a privilege of liquid crystalline polymers, their generally high melt viscosity presents a major challenge to processing into large-area thin films. To combine ease of material processing with glass-forming ability in discrete molecular systems, extensive efforts have been made over the last two decades to develop glass-forming liquid crystals (GLCs) with well-defined structures having low to medium molecular weights (see for example Wedler, W. et al., 1991, J. Mater. Chem., 1, 347; Attard, G. S. et al., 1992, Chem. Mater., 4, 1246; Neumann, B. et al., 1997, Adv. Mater., 9, 241; and Gresham, K. D. et al., 1994, J. Polym. Sci: Part A: Polym. Chem., 32, 2039). Applications that have been explored with various GLCs include: optical data storage (see for example Ortler, R. et al., 1989, Marromol. Chem., Rapid Commun, 10, 189; and Tamaoki, N. et al., 1997, Adv. Mater., 9, 1102), optical nonlinearity (see for example Wang, H. et al., 1996, Nature, 384, 244; and Loddoch, M. et al., 1994, Appl. Phys. B, 59, 591), photochromism (see for example Natarajan, L. V. et al., 1991, Macromolecules, 24, 6554), tunable filters for optical communication (see for example Morita, Y. et al., 1999, Jpn. J. Appl. Phys., 38, Part.1, 95), and viewing angle compensation for displays (see for example Van de Witte, P. et al., 1999, Liquid Crystals, 26, 1039).
The present invention is directed to a glass-forming liquid crystal composition comprising a compound having a molecular weight in the range of about 1000 to 5000 grams per mole, and having the formula
(NEM)xxe2x80x94CYCxe2x80x94(CHI)y 
wherein CYC is a substituted cycloaliphatic core moiety containing about 24 to about 60 carbon atoms or a substituted aromatic core moiety containing about 6 to about 36 carbon atoms, NEM is a nematogenic pendant moiety, CHI is a chiral pendant moiety, x is 3 to 9, and y is 0 to 4. The invention is further directed to an optical device formed from the liquid crystal composition.